1. Field of the Invention
The present invention relates to an ink-jet recording apparatus in which ink drops are ejected so as to be deposited on a surface of recording paper only when recording is required. In particular, the present invention relates to a small-sized high-density ink-jet recording apparatus produced through application of a micro-machining technique, and relates to a method for producing an ink-jet head as a main part of such an ink-jet recording apparatus.
2. Description of the Prior Art
Ink-jet recording apparatuses are advantageous in many points that noise is extremely low at the time of recording, high-speed printing can be made, the degree of freedom of ink is so high that inexpensive ordinary paper can be used, and so on. Among those ink-jet recording apparatuses, an ink-on-demand type apparatus in which ink drops are ejected only when recording is required has been the focus of attention because it is not necessary to recover ink drops unnecessary for recording.
In such an ink-on-demand type apparatus, as described, for example, in Japanese Patent Postexamin. Publication No. Hei-2-51734, a print head is constituted by: a plurality of nozzle openings arranged in parallel to each other to eject ink drops therefrom; a plurality of independent ejection chambers respectively communicated with the corresponding nozzle openings and each having walls one of which is partly formed to serve as a diaphragm; a plurality of piezoelectric elements respectively attached on the corresponding diaphragms so as to serve as electromechanical transducers; and a common ink cavity for supplying ink to the each of the ejection chambers. In such a print head, upon application of a printing pulse voltage to any one of the piezo electric elements, the diaphragm corresponding to the one piezoelectric element is mechanically distorted so that the volume of the ejection chamber corresponding to the diaphragm is reduced and the pressure in the chamber is increased instantaneously. As a result, an ink drop is ejected from the corresponding one of the nozzle openings toward recording paper.
In the aforementioned structure of the conventional ink-jet recording apparatus, however, much labor as well as much time are required for mounting such piezoelectric elements on the ejection chambers because the piezoelectric elements must be stuck onto the outside of the ejection chambers through glass or resin plates forming the diaphragms or must be arranged in the inside of the ejection chambers. Particular in the latest printers, both a high speed and a high printing quality are required so that there is a tendency that the number of the nozzle openings for ejecting ink drops are increased. Piezoelectric elements corresponding to the nozzle openings are machined by dicing or by means of a wire saw and then placed in predetermined positions through an adhesive agent or the like. In the case of a high-density ink-jet recording apparatus having a large number of nozzle openings, if machining is required to provide the piezoelectric elements, there is a limitation from the viewpoints of machining capability, mechanical accuracy and dimensional accuracy.
Further, there have been distortion errors of the piezoelectric elements due to scattering in production of piezoelectric elements per se, and in some cases, there have been occurrence of variations in ink ejection speed from the respective nozzle openings.
Further, electrodes for driving the piezoelectric elements are respectively formed in the piezoelectric elements per se and then the piezoelectric elements are stuck onto a substrate through an adhesive agent. Accordingly, not only the electrodes must be formed individually in the respective piezoelectric elements but the driving efficiency of the ink-jet recording apparatus is lowered because an adhesive agent layer is interposed between the substrate and the piezoelectric elements so that it is difficult to extend the lifetime of the ink-jet recording apparatus.
Other than the above system in which the diaphragms are driven by the piezoelectric elements, there is a system in which the ink in the ejection chambers is heated (Japanese Patent Postexamin. Publication No. Sho-61-59911). In this system, specifically, the ink in the ejection chambers is heated by a heater so that the pressure in the ejection chambers is increased by the generation of bubbles caused by evaporation of the ink to thereby eject ink drops from the chambers. This heating system has an advantage in that heating resistors can be formed of thin-film resistors of TaSiO.sub.2, NiWP or the like by sputtering, CVD, evaporating deposition, plating, or the like. The system, however, has a problem in that the lifetime of the head itself is short because the heating resistors are damaged by repetition of heating/quenching and shock at the time of the breaking of bubbles in the ink.